Obturating piston for an automatic weapon with a gas-bleed passage



-1 1967 E. MUHLEMAN-N 3,33 9

OBTURATING PISTON FOR AN AUTOMATIC WEAPON WITH A GAS-BLEED PASSAGE Filed Oct. 19, 1965 2 Sheets-Sheet 1 Fig.1 I III so: 204

g- 1967 E. MUHLEMANN 3,333,509 OBTURATING PISTON FOR AN AUTOMATIC WEAPON WITH A GAS-BLEED PASSAGE Filed Oct. 19, 1965 2 Sheets-Sheet 2 In vehfor fr/ysf MdA/smann United States Patent 3,333,509 OBTURATING PISTON FOR AN AUTOMATIC WEAPON WITH A GAS-BLEED PASSAGE Ernst Miihlemann, Zurich, Switzerland, assignor to Oerlikon-Buhrle Holding A.G., Zurich, Switzerland Filed Oct. 19, 1965, Ser. No. 497,946 Claims priority, application Switzerland, Oct. 20, 1964, 13,620/ 64 4 Claims. (Cl. 89-493) ABSTRACT OF THE DISCLOSURE Automatic weapon wherein a gas bleed passage leads from an exchangeable barrel to a pressure chamber in a receiver. In the receiver there is provided an obturating piston at the separating point between the gas-bleed passage in the barrel and the pressure chamber in the receiver. This obturating piston has two opposite faces. One of these faces is forced against a surface of the barrel and the other face is a part of a back pressure chamber. The gas-pressure in the back pressure chamber forces the obturating piston against the surface of the barrel.

This invention relates to an automatic fire arm wherein a connection between the gas bleed in an exchangeable barrel and a passage in a receiver leading to a gas pressure chamber contains a longitudinal bored obturating piston.

In an automatic firearm of this type, both the cylindrical bore in the receiver and the obturating piston arranged coaxially to it in the wall of the barrel are set at an angle to the axis of the barrel. Since the piston dimensions are determined both by the dimensions of the bore and by the length of the guiding surface of the piston, it must not fall below a certain minimum value. Such an embodiment of an automatic firearm as shown in the prior art has the disadvantage that it can not be used for small calibre firearms having thin barrel walls. Furthermore, in another embodiment of an automatic firearm of the prior art, the gas-bleed passage is located directly below the surface of the barrel so that no obturating piston can be fitted except where an extra part is fitted to the barrel to accommodate such a piston, which involves an increase in production costs.

An object of the present invention is to improve firearms so that a reliable and effective obturation is obtained at the separating point between the gas passage in the barrel and the bore in the receiver.

A further object of the invention is to provide an obturating piston located in the receiver which is pressed against the outer surface of the barrel by the gas pressure in a back pressure chamber located at the downstream side of the piston.

With the above and other objects in view which will become apparent from the detailed description below, some preferred embodiments are shown in the drawings in which:

FIGURE 1 is a partial longitudinal cross section of an autoamtic firearm taken upon section line I-I of FIG. 2.

FIGURE 2 is a partial plan view of a portion of the firearm shown in FIGURE 1.

FIGURE 3 is a cross-sectional view taken along section line IIIIII of FIGURE 1 looking in the direction of the arrows, and

FIGURE 4 shows a partial view corresponding to the view shown in FIGURE 1 of an alternative embodiment of the invention.

Referring to FIGURES 1, 2 and 3 of the drawings, a barrel is inserted in a receiver 11 and is maintained in such receiver in the position shown in FIGURE 1 by means of a bayonet slot joint 12. A pin 13 inserted at the bottom of the receiver 11 engages the joint 12 so as to lock the barrel 10 in an angular position relative to the receiver.

The receiver 11 is provided with a housing 14 into which an insert 15 is screwed. The insert 15 has a cylindrical chamber 16 wherein the gas piston 17 reciprocates. The gas piston 17 transmits its motion to the mechanism for unlocking the breech mechanism of the firearm via the piston rod 18 in the well known manner which is therefore not described. At the front end of the piston 15 at the left as shown in FIGURES 1 and 2, a block 151 has two mutually perpendicular bores 23 forming the back pressure chamber and 29 forming a part of the gas bleed passage connecting the chamber 16 with the concave cylindrical surface 152 of the block 151 extending longitudinally over the surface of the barrel as shown more particularly in FIGURE 3.

The bore 28 which is arranged perpendicular to the longitudinal axis of the barrel widens conically at 283 to the diameter of its coaxial continuation 284 prior to the junction with the bore 29 extending parallel to the barrel. A regulating needle 30 is screwed into the bore 284 and extends to the upper surface of the block 151. The tip 301 of the regulating needle 30 has the same shaped cone as the portion 283 and forms the front end of a cylindrical portion 302 whose diameter is less than that of the main body of the needle 30. The total crosssectional area of the annular space surrounding the needle tip 301 is less than that of the section 282 of the drillway between the obturating piston 19 and the conical widening 283. The rate of fire of the firearm can be simply controlled by screwing in and out of the regulating needle 30 so as to vary the cross-sectional area of this throttle point.

The cylindrical obturating piston 19 has a smooth peripheral surface and makes a close sliding fit in the enlarged part 281 of the bore 28 so that its concave end surface 192 which adjoins the outer surface of the barrel lies against the surface 213 of the insert 21 which is flush with the barrel surface when the obturating piston is in the firing position as shown in FIGURES 1 and 3.

A pin 31 is located in a bore extending at right angles to the longitudinal axis of the barrel and engages with a flat portion 194 provided in the side of the obturating piston 19. The pin 31 prevents the obturating piston 19 from falling out when the firearm is dismantled and also prevents rotation thereof about its axis but permits the piston 19 to have a limited longitudinal stroke. The bore 191 through the piston 19 has a conical bell-mouth extending to the flat end surface 193 of the piston 19.

When a bullet has passed the gas port in the barrel the explosion gases pass along the bleed passage to the obturating piston, then through the bore 191 to the bores 28 and 29 of the block 15 and then to the gas piston 17. The restriction to the gas flow at the throttle point at the tip 301 of the regulating needle 30 creates a back pressure which acts on the end surface 193 of the obturating piston 19 and presses it downwardly against the surface of the barrel and more particularly on the surface 213 of the insert 21 so as to obturate the gap separating the barrel 10 from the receiver 11 and prevent gas from leaking out.

In the embodiment of the invention shown in FIGURE 4 the block 15 contains an exchangeable hard metal jet 32 placed between the obturating piston 19 and the bore 29. The bore provided in the jet 32 is of smaller diameter than the bore 191 in the obturating piston thereby creating the back-pressure required to act upon the end-face 193 of the piston and determine the rate of fire of the firearm.

In both the embodiment of the invention illustrated in FIGURE 1 and that shown in FIGURE 4, the back pressure space between the end-face 193 of the obturating piston and the throttle point is so small that the gaspressure becomes effective at once and the piston 19 is forced downwards against the surface 213 of the insert or the barrel so as to create obturation immediately after the ingress of explosion gases into the block 15.

The foregoing description refers to a firearm in which the obturating piston is perpendicular to the axis of the barrel. It will clearly be seen that the principle of the invention is by no means restricted to obturating pistons orientated in this direction, but may also be applied to obliquely angled obturating pistons or those running par allel to the gun barrel.

I claim:

1. An automatic weapon comprising an exchangeable barrel having an outer surface and a gas-bleed passage, a receiver containing a pressure chamber, a connection between said gas-bleed passage and said pressure chamber, a back pressure chamber in said connection, an axially perforated obturating piston located in said connection having two opposite faces, one of said faces adapted to be forced against said surface and the other of said faces forming a part of said back-pressure chamber, and means for providing gas-pressure in said back pressure chamber to force said obturating piston against said surface.

2. An automatic firearm as set forth in claim 1 wherein said back pressure chamber has an exit in the form of a jet and a regulating needle for varying the crosssectional area of said exit.

3. An automatic firearm as set forth in claim 1 wherein said back pressure chamber has an exchangeable restriction jet located at the exit therefrom.

4. An automatic weapon as set forth in claim 1 wherein said barrel has an insert between said barrel and said obturating piston and said obturating piston is forced against said insert.

References Cited UNITED STATES PATENTS 1,431,057 10/1922 Sutter 89--130 2,818,785 1/1958 Maillard 89193 2,873,650 2/1959 Pinkerton 89131 FOREIGN PATENTS 191,769 9/1957 Austria.

BENJAMIN A. BORC'HELT, Primary Examiner.

S. C. BENTLEY, Assistant Examiner. 

1. AN AUTOMATIC WEAPON COMPRISING AN EXCHANGEABLE BARREL HAVING AN OUTER SURFACE AND A GAS-BLEED PASSAGE, A RECEIVER CONTAINING A PRESSURE CHAMBER, A CONNECTION BETWEEN SAID GAS-BLEED PASSAGE AND SAID PRESSURE CHAMBER, A BACK PRESSURE CHAMBER IN SAID CONNECTION, AN AXIALLY PERFORATED OBTURATING PISTON LOCATED IN SAID CONNECTION HAVING TWO OPPOSITE FACES, ONE OF SAID FACES ADAPTED TO BE FORCED AGAINST SAID SURFACE AND THE OTHER OF SAID FACES FORMING A PART OF SAID BACK-PRESSURE CHAMBER, AND MEANS FOR PROVIDING GAS-PRESSURE IN SAID BACK PRESSURE CHAMBER TO FORCE SAID OBTURATING PISTON AGAINST SAID SURFACE. 